分子筛硅／铝比对Cu-ZnO-Al2O3／HMCM-22催化合成二甲醚反应性能的影响

以六亚甲基亚胺为模板剂,采用动态水热晶化法合成了不同硅/铝比的HMCM-22分子筛,并以其为甲醇脱水活性组分与铜基甲醇合成活性组分(Cu-ZnO-Al2O3)组成双功能催化剂,在连续流动加压固定床微型反应器上考察了其对合成气直接制二甲醚反应的催化性能. 结果表明,随着HMCM-22分子筛硅/铝比的增大, CO转化率变化不大,但CO2和烃类副产物的生成量逐渐减少,从而导致目的产物二甲醚的选择性和收率均逐渐升高. 氨程序升温脱附和吡啶吸附红外光谱表征结果表明,随着分子筛硅/铝比的增大, HMCM-22分子筛的酸中心的数量逐渐减少.

Influence of SiO2/Al2O3 Ratio in HMCM-22 on Catalytic Performance of Cu-ZnO-Al2O3/HMCM-22 for Synthesis of Dimethyl Ether

A series of HMCM-22 zeolite samples with different SiO2/Al2O3 ratios were hydrothermally synthesized with hexamethyleneimine as a template and mechanically mixed with Cu-ZnO-Al2O3(a methanol synthesis component) to form bifunctional catalyst.The direct synthesis of dimethyl ether(DME) from syngas was carried out over the bifunctional catalyst in a fixed-bed reactor under pressurized continuous flow conditions.The results indicated that the selectivity for CO2 and hydrocarbons decreased with the increase of SiO2/Al2O3 ratios in HMCM-22 zeolite,so the selectivity for DME was enhanced greatly. By combining the catalytic performance with the acidity of HMCM-22 zeolite characterized by pyridine-adsorbed IR and NH3 temperature-programmed desorption,the decrease in the amount of CO2 and hydrocarbons could be attributed to the significant decrease in the amount of acid sites on the HMCM-22 zeolite surface with the increase of SiO2/Al2O3 ratios.